1. Technical Field
The invention relates to an optical element and an optical unit.
2. Description of the Related Art
Various optical lenses for use in an optical unit have been developed in accordance with reduction of the optical unit in size and weight and multiple functions of the optical unit. For example, in an optical unit for use in a cellular phone having a camera function or a vehicle rear-view monitor, wide-angle lenses having a view angle equal to or larger than a view angle (about 45 to 50 degrees) of a standard lens are frequently used. Particularly, in an optical unit for use in a cellular phone, optical lenses having wide view angels, which have not been used conventionally, are used as the cellular phones becomes thin.
Accordingly, there is the case where unintended light having an incidence angle larger than that of a general wide-angle lens is incident on the optical lens and is reflected inside the optical lens, the optical unit, and the like. As a result, flare, ghost, or the like may be generated. When the flare is generated, the contrast of the original image is reduced or colors in a color picture become dull due to light that does not contribute to image formation. Also, when the ghost is generated, a false image or multiple images of an object are observed through the optical unit due to light that contributes to image formation.
Since a processing accuracy required for an optical lens is improved, when an surface located on the outer side with respect to an optical functional surface of an optical lens is processed with the same degree in accuracy as that for the optical functional surface, internal reflection of the light incident on the optical lens is enhanced, which is one cause of generation of the flare or the like. The optical functional surface of the optical lens represents a range, up to an outer side, including a range of an effective diameter (diameter, in a section perpendicular to an optical axis, of a bundle of parallel light, which comes from a point at infinity on the optical axis and passes the optical lens) of the optical lens. It is difficult to process an optical lens in accordance with a designed shape for implementing the function of the optical lens, in a molding process only for the range of the effective diameter. Therefore, the optical functional surface means a range which is molded in accordance with a predetermined designed shape for implementing a function as an optical lens as well as the range of the effective diameter. Generally, similarly to a portion within the effective diameter, a portion of the optical functional surface outside the effective diameter is molded to have a shape and surface accuracy that can provide a predetermined optical function by refracting incident light.
In order to solve these problems, for example, JP 2002-303703 A discloses the following solutions: As a first solving method, JP 2002-303703 A proposes blocking light so as not to enter through a portion shielded by a light shielding plate or a concave surface by making the light shielding plate that surrounds a lens surface to protrude toward a front side of the lens surface or by providing the optical lens within the concave surface that surrounds the lens surface. Also, as a second solving method, JP 2002-303703 A proposes blocking light so as not to enter through a portion in which a light shielding film is formed, by forming the light shielding film in a portion of the lens surface where light shielding is required. Furthermore, as a third solving method, JP 2002-303703 A proposes, when it is applied to a lens array, blocking light so as not to enter through a portion where a rough surface portion is formed, by forming the rough surface portion in a lens adjacent portion of the optical lens which requires light shielding so that the rough surface portion scatters the light.
However, the first solving method results in that the manufacturing cost increases as an additional component for forming the light shield plate or the concaved part is used while a request for thinning and lightening the optical unit cannot be achieved. Also, the second or third solving method blocks incident light from a portion of the lens surface that requires light shield. However, when light having a large incident angle which is a cause of the flare or the like is incident in the effective diameter of the lens, light originally required for forming an image is blocked as well as unintended light. Accordingly, it is difficult to fully solve these types of problems only by controlling light incident on the optical lens.
Thus, a method for controlling internal reflection of light incident on the optical lens is applied instead of or in addition to controlling of the light incident on the optical lens. For example, it may be conceived that an antireflection film is formed on a surface which reflects the incident light and which includes the optical functional surface. In this case, the antireflection film is formed by printing, film adhesion, deposition or exposure on the surface including the optical functional surface of the optical lens molded by an injection molding method or a press molding method. However, when the printing or the film adhesion is used, an accuracy of the formed reflection film is low and it is difficult to manage its quality. On the other hand, when the deposition or the exposure is used, the manufacturing cost for forming the antireflection film increases. Also, when any of these methods is used, a secondary process after molding of the optical lens is required. Therefore, it is inevitable that manufacturing process becomes complex and that the manufacturing cost increases.